Although the concept of suppression mediated by T lymphocytes was originally proposed more than 30 years ago, recent studies in animal models of autoimmunity have rekindled interest in the existence of defined subsets of T cells that suppress immune responses. Several populations of suppressor/regulatory T cells have been defined in rodents and man, including the naturally-occurring CD4+CD25+ and the IL-10-induced T regulatory 1 cells. Determination of the cellular target and the molecular basis of T cell-mediated suppression is a major area of current research. The nature of the physiologic ligand recognized by these cells is also unknown as is the breadth of their T cell repertoire. Suppressor/regulatory T cells have been primarily been shown to inhibit animal models of autoimmune disease. However, recent studies have extended their range of activities to inhibition of tumor immunity, graft rejection, allergic disease, graft versus host disease, and acute and chronic infectious diseases. One critical area of future study will involve the development of protocols to enhance suppressor/regulatory T cell function in vivo by pharmacologic means as such as approach should prove useful in autoimmunity, allergic disease, and graft rejection. Similarly, a related area will involve inhibition of regulatory T cell function, either transiently or permanently, by pharmacologic manipulation or treatment of animals or man with monoclonal antibodies specific for effector molecules on these cells. Protocols are now being developed for adoptive immunotherapy using suppressor/regulatory T cell. These cells will be administered to patients with GVHD, graft rejection, and organ-specific and systemic autoimmune disease. The proposed meeting will review all of the above issues and focus on the manipulation of suppressor/regulatory T cell function in animal models of human disease as well as in clinical situations. The manipulation of suppressor/regulatory T cell function in clinical situations is still relatively unexplored and the meeting will offer the opportunity to discuss and compare different approaches to address this issue. The rapidly evolving field of suppressor/regulatory T cell manipulation, with all its implications for human health, makes this conference particularly timely and important for the future development of the field. Attendance at this conference will be highly relevant to the careers of graduate students and post-doctoral fellows active in the field.